Date:   Sat, 11 Feb 2023 22:10:23 -0500
From:   Kent Overstreet <kent.overstreet@linux.dev>
To:     Alan Stern <stern@rowland.harvard.edu>
Cc:     Kent Overstreet <kent.overstreet@gmail.com>,
        Linus Torvalds <torvalds@linux-foundation.org>,
        Coly Li <colyli@suse.de>,
        Tetsuo Handa <penguin-kernel@i-love.sakura.ne.jp>,
        syzkaller <syzkaller@googlegroups.com>,
        Dmitry Vyukov <dvyukov@google.com>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        "Rafael J. Wysocki" <rafael@kernel.org>,
        Peter Zijlstra <peterz@infradead.org>,
        Ingo Molnar <mingo@redhat.com>,
        Boqun Feng <boqun.feng@gmail.com>,
        LKML <linux-kernel@vger.kernel.org>,
        USB list <linux-usb@vger.kernel.org>,
        Hillf Danton <hdanton@sina.com>
Subject: Re: [PATCH RFC] drivers/core: Replace lockdep_set_novalidate_class()
 with unique class keys
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On Sat, Feb 11, 2023 at 10:03:11PM -0500, Alan Stern wrote:
> On Sat, Feb 11, 2023 at 09:46:42PM -0500, Kent Overstreet wrote:
> > On Sat, Feb 11, 2023 at 09:40:58PM -0500, Alan Stern wrote:
> > > Or maybe you're referring to what this patch does?  It does indeed 
> > > create a bunch of dynamic classes -- one for each struct device.  The 
> > > ordering rules derived by lockdep will be somewhat arbitrary, as you 
> > > say.  But some of them certainly will be related to the structure of the 
> > > source code.
> > 
> > I could be :) I haven't been able to find the patch in question - have a
> > link?
> 
> It was earlier in this email thread.  Here's a link:
> 
> https://lore.kernel.org/r/Y+gLd78vChQERZ6A@rowland.harvard.edu/
> 
> > If you're talking about making lock_class_key dynamic, I think I stand
> > by what I said though - OTOH, if all you're doing is lifting that to the
> > caller of the device object init function, so it'll still be a static
> > object in the driver, that would be totally fine.
> 
> The patch does the first, not the second.  Feel free to object some 
> more...  :-)

So IMO the more correct way to do this would be to change
device_initialize() to __device_initialize(), have it take a
lock_class_key as a parameter, and then use __mutex_init() instead of
mutex_init().

But let's think about this more. Will there ever be situations where
lock ordering is dependent on what hardware is plugged into what, or
what hardware is plugged in first?